Seismic Assessment of an Irregular Base Isolated Hospital

Abstract eng:
The present paper discusses the results of extensive dynamic analyses carried out on a large irregular base isolated hospital building, under construction in Naples, Italy. The framed structure of the multi-storey building is assumed as a sample system to assess the reliability of linear and non linear dynamic analyses implemented in modern codes of practice world-wide and they conservatism, if any. In so doing, a suite of spectrum compatible natural records are utilized to perform linear and non linear response analyses. The results of such analyses are then compared with simplified methods based on single-degree-of-freedom approximations. It is found that the selection of adequate natural records from existing earthquake catalogues is not straightforward, especially for base isolated structures which are affected chiefly by long distance and high magnitude events. A non linear model to simulate the dynamic response of rubber bearings is also presented and issues related to the calibration of such model are also highlighted; these calibrations are significantly affected by the fundamental frequency of vibration of the sample structural system. It is concluded the linear analyses may underestimate the displacements of the devices in base isolated structures when compared with non linear response analyses. To enhance the reliability of the analysis results, it is of paramount importance to calibrate the dynamic response of the rubber isolators on the fundamental frequency of vibration of the base isolated framed system and to select long distance and high magnitude pairs ground motions from existing catalogues of earthquakes, if available.

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